In a 5 to 3 ruling, the U. S. Supreme Court on Monday invalidated three of four challenged provisions of Arizona’s controversial immigration law, but  left standing a key “show me your papers” provision, which requires police to check the immigration status of individuals they detain for another reason and suspect of being in the country illegally.  Arizona passed this law in 2010 but most provisions were blocked last year by a decision of the U.S. Court of Appeals for the 9th district.

Overall, the ruling reinforced the federal government’s primacy in immigration policy.  Justice Anthony M. Kennedy, writing for the majority, said “Arizona may have understandable frustration with the problems caused by illegal immigration, but the state may not pursue policies that undermine federal law.”

“The Federal Government has brought suit against a sovereign state to challenge the provision even before the law has gone into effect,” the court said.  “At this stage without the benefit of a definite interpretation from the state courts, it would be inappropriate to assume the law will be construed in a way that creates a conflict with federal law.” The decision upholding the “show me your papers” provision came with a warning that the courts will be watching its implementation.  “This opinion does not foreclose other preemption and constitutional challenges to the law as interpreted and applied after it goes into effect,” Kennedy wrote.

Five states have adopted laws similar to Arizona’s, and others are waiting in the wings.

The court threw out the section of the law that made it a misdemeanor for immigrants to fail to carry registration or identification documents.  The court also ruled that the state cannot criminalize that act of an illegal immigrant  seeking employment, saying the Arizona law went beyond federal law by making it a criminal penalty, rather than civil, which is federal law in this case.  In addition, the state cannot authorize state officers to arrest someone on the belief that the person has committed an offense that makes him deportable.  In that case, the court said states cannot impose their own penalties for federal crimes as they “would conflict with the careful framework Congress adopted.”

Kennedy wrote for Chief Justice John G. Roberts Jr. and Justices Ruth Bader Ginsburg, Stephen G. Breyer, and Sonia Sotomayor.  Justice Elana Kagan recused herself from the case.

Justices Scalia, Clarence Thomas, and Samuel A. Alito, Jr. wrote dissents from the decision, arguing that the whole law should have been upheld.  “Arizona has moved to protect its sovereignty–not in contradiction of federal law, but in complete compliance with it,” Scalia wrote.  “If securing its territory in this fashion is not within the power of Arizona, we should cease referring to it as a sovereign state.”